1. Field of the Invention
The invention concerns a lighting or signalling device for motor vehicles in which the light source is produced by means of light emitting diodes. The invention also concerns a motor vehicle comprising such a lighting or signalling device.
The invention finds applications in the automotive field and, in particular, in the field of lighting and signalling for motor vehicles.
2. Description of the Related Art
Generally a motor vehicle comprises at least two lighting devices situated at the front of the vehicle, also called headlights, and signalling devices situated at the front and rear of the vehicle. Each lighting or signalling device comprises a housing closed by a protective lens and equipped firstly with a light source emitting a light beam and secondly optical elements for directing this light beam. Currently, in the majority of lighting or signalling devices, the light source is produced by means of a lamp, such as a discharge lamp, halogen lamp etc. Lighting and signalling devices therefore each comprise a single lamp or possibly two lamps for main-beam lighting.
These lamps have the advantage of having a high efficiency and high luminance. However, they have the drawback of emitting a high level of heat locally. Consequently they each constitute in the lighting or signalling devices, a source of heat with a very hot single concentrated point. For example, in the case of a halogen lamp, the filament of the lamp has a temperature of around 3,000° C., the glass balloon of the bulb has a temperature above 400° C. and the bulb cap has a temperature around 200° C. These lamps also have the drawback of emitting infrared rays.
Moreover, in order to increase further their light yield and to direct their light beams, these lamps are generally placed close to a mirror. This mirror is conventionally metal or metallised, which further concentrates the heat and infrared rays emitted by the lamp. In addition, these infrared rays are directed towards the exit face of the lighting or signalling device, namely the protective lens, which heats up under the effect of these rays. In addition, if the protective lens is dirty, the lens absorbs these infrared rays instead of transmitting them, which concentrates the heat further. Consequently the protective lens of the device must be produced from a material that is particularly resistant to heat.
The casings of the lighting or signalling devices must be perfectly impervious to ambient moisture, in particular rain, snow, etc. It is therefore difficult to ventilate the inside of the housing in order to cool it.
In order to resolve these problems of concentrated heat, it is possible to produce light sources using light emitting diodes. Such a light source is produced by means of a plurality of light emitting diodes, or LEDs, associated in modules and mounted on a fixed or movable plate. The temperature attained by a light emitting diode is around 100° C. to 150° C. Such a light source has the advantage of offering high efficiency, able to achieve that of conventional lamps, and where the heat is distributed over all the modules. This is because, the light emitting diodes being grouped together in modules within the housing, the light source is formed from several luminous points distributed in the whole of the housing. The heat emitted by the light source is therefore distributed in the whole of the housing, which avoids the existence of a single concentrated heat point.
In addition, the distribution of the luminous points in the housing makes it possible to direct the corresponding light beams in the required directions, without necessarily using an enveloping mirror. The heat emitted by such a light source is thus dispersed rather than shielded.
In addition, light emitting diodes are electronic components which have the advantage of not emitting near infrared rays (in the range 1 to 5 μm), which locally minimises the heat emitted by the light source.
However, even if the temperature of a light emitting diode is relatively low compared with the temperature of a conventional lamp and even if the hot spots are distributed in the housing, it is also necessary to cool such a light source. In order to cool electronic components, and in particular power diodes, it is known how to mount the component to be cooled on a radiator or heat sink. A radiator or heat sink is associated with each component. The component is then cooled with ambient air. In the case where the component is a light emitting diode mounted in a vehicle lighting or signalling device, the ambient air is the air of the housing of the device. It is therefore relatively hot (at a temperature around 95° to 100° C.). It is consequently necessary to use a radiator or heat sink of relatively large size in order to cool this component sufficiently.
The use of such a radiator or heat sink can be envisaged when the plate on which the light emitting diodes are mounted is fixed. However, in the majority of current vehicles, the light source is orientable to allow correction of the light range. In particular, with a DBL (Bending Light) system, the light source must be able to be oriented to the right or to the left of the vehicle so that the lighting follows the path of the road. The light source can also be orientable towards the top or bottom of the vehicle in order to take account of the attitude of the vehicle. In these cases, the light emitting diodes are mounted on a movable plate, moved by a motor. However, if each light emitting diode must be mounted on the movable mounting plate with the radiator or heat sink, of relatively large size, which is associated with it, then the movable plate becomes heavy and the motor moving it must be powerful.
In order to limit the weight of the movable mounting plate, it is envisaged dividing the light source into several modules, each module comprising its own movable plate. In this case, it is possible to use less powerful motors for each module. On the other hand, it is necessary to use one motor for each movable mounting plate, which considerably increases the cost of each device. In addition, the use of several motors simultaneously causes a problem of slaving the assembly to an initial position.
In order to improve the cooling of the electronic components, and in particular the power diodes, the document U.S. Pat. No.-B2-6,639,360 proposes associating fans with the radiators or heat sinks. More precisely, this document proposes to place, under each light emitting diode, a radiator or heat sink with which there is associated a fan providing a circulation of air propagated by the radiator or heat sink. In this case, each radiator or heat sink must be of smaller dimensions. However, the weight saved by the use of a smaller radiator or heat sink is at least partly compensated for by the addition of a fan. The problem of weight of the movable plate to be moved remains identical to the problems stated above.
There is, therefore, a need to provide a lighting and signalling device that overcomes one or more of the problems in the prior art.